1. Field of the Invention
The present invention relates to a magnetic recording medium that can be incorporated within a magnetic storage apparatus such as a hard disk drive (HDD), for example. In particular, the invention relates to a method of detecting a minute protrusion existing on the surface of a magnetic recording medium.
2. Description of the Prior Art
Japanese Patent Application Publication No. 9-063050 discloses a conventional inspection apparatus capable of detecting protrusions existing on a magnetic recording disk. The inspection apparatus includes a flying slider opposed to the surface of a rotating magnetic recording disk. A piezoelectric element such as a PZT (lead zirconate titanate) element is mounted on the flying slider. When the flying slider collides against a protrusion on the surface of the magnetic recording disk, sound or an elastic wave is generated. The PZT element serves to convert the sound of the collision into an electric signal. A voltage signal is output from the PZT element. When the voltage signal exceeds a predetermined amplitude, a protrusion is detected.
A further improved recording density is expected in a hard disk drive, for example. The flying height of a head slider is required to get reduced. The head slider is forced to get closer to the surface of the magnetic recording disk. It is required to reduce the height of protrusions on the magnetic recording disk. The aforementioned predetermined amplitude or threshold level is required to get smaller so as to reduce the height of a protrusion to be detected in the inspection apparatus.
Noise is often included in the voltage signal output from the PZT element. If the noise exceeds a predetermined amplitude, the inspection apparatus may take it for the existence of a protrusion. A reduced threshold level may cause an increased probability of the misidentification for a protrusion.